/*
*	ID : pallab81
* 	PROG : 25D
* 	LANG : C++
* 	2012-08-29-12.41.24 Wednesday
*
* 	"I have not failed, I have just found 10000 ways that won't work.
*/

#include <iostream>
#include <algorithm>
#include <vector>
#include <sstream>
#include <fstream>
#include <string>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <functional>
#include <bitset>
#include <iomanip>

#include <ctime>
#include <cassert>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <climits>
#include <cstring>
#include <cstdlib>

using namespace std;


#define foR(i1,st,ed) for(int i1 = st , j1 = ed ; i1 < j1 ; ++i1 )
#define fo(i1,ed) foR( i1 , 0 , ed )
#define foE(i1,st,ed) foR( i1, st, ed+1 )
#define foit(i, x) for (typeof((x).begin()) i = (x).begin(); i != (x).end(); i++)
#define bip system("pause")
#define Int long long
#define pb push_back
#define SZ(X) (int)(X).size()
#define LN(X) (int)(X).length()
#define mk make_pair
#define SET( ARRAY , VALUE ) memset( ARRAY , VALUE , sizeof(ARRAY) )
#define line puts("")

template<class T1>
inline void debug(T1 _x) {
    cout<<_x<<'\n';
}
template<class T1, class T2>
inline void debug(T1 _x,T2 _y) {
    cout<<_x<<' '<<_y<<'\n';
}
template<class T1, class T2, class T3>
inline void debug(T1 _x,T2 _y,T3 _z) {
    cout<<_x<<' '<<_y<<' '<<_z<<'\n';
}
template<class T1, class T2, class T3, class T4>
inline void debug(T1 _x,T2 _y,T3 _z,T4 _zz) {
    cout<<_x<<' '<<_y<<' '<<_z<<' '<<_zz<<'\n';
}
template< class T1>
inline void debug(T1 _array,int _size) {
    cout<<"[";
    for (int i=0; i<_size; ++i) {
        cout<<' '<<_array[i];
    }
    puts(" ]");
}
inline bool CI(int &_x) {
    return scanf("%d",&_x)==1;
}
inline bool CI(int &_x, int &_y) {
    return CI(_x)&&CI(_y) ;
}
inline bool CI(int &_x, int &_y, int &_z) {
    return CI(_x)&&CI(_y)&&CI(_z) ;
}
inline bool CI(int &_x, int &_y, int &_z, int &_zz) {
    return CI(_x)&&CI(_y)&&CI(_z)&&CI(_zz) ;
}
inline void wait( double seconds ) {
    double endtime = clock()+( seconds* CLOCKS_PER_SEC );
    while( clock() < endtime ) {
        ;
    }
}
#if !defined( ONLINE_JUDGE )
    #define debug
#endif
const int mxn = 1000006;

char str[mxn];
inline void read() {
    gets(str);
}

namespace KMP {
char prefix[mxn];
inline void get_prefix_string(char *s) {
    sprintf(prefix,"%s",s);
}
int pi[mxn];
inline void build_fail_fun() {
    int n = strlen(prefix);
    SET(pi,0);
    for(int i=1; i<n; ++i) {
        int j = pi[i-1];
        while (j > 0 && prefix[i] != prefix[j]) {
            j = pi[j-1];
        }
        if (prefix[i] == prefix[j]) {
            ++j;
        }
        pi[i] = j;
    }

}
}
inline void proc() {
    KMP::get_prefix_string(str);
    KMP::build_fail_fun();
#if defined( debug )
    puts( KMP::prefix );
    fo(i, strlen(KMP::prefix) ) {
        cout<< KMP::pi[i];
    }
    line;
#endif
    int len = strlen( KMP :: prefix );

    if( KMP::pi[ len-1 ] ==0 ){
        puts("Just a legend");
        return ;
    }
    foR(i,1,len-1 ){
        if( KMP::pi[i]==KMP::pi[len-1] ){
            KMP::prefix[ KMP::pi[i] ] = '\0';
            puts(KMP::prefix);
            return ;
        }
    }
    if( KMP::pi[ KMP::pi[len-1]-1 ] ==0 ){
        puts("Just a legend");
        return ;
    }
    KMP::prefix[ KMP::pi[ KMP::pi[len-1]-1  ] ]='\0';
    puts(KMP::prefix);

}
int main() {
    int t=1;
#if !defined( ONLINE_JUDGE )
    freopen("in","r",stdin);
    t=4;
#endif
    while(t--) {
        read();
        proc();
    }
    return 0;
}
